Mancozeb is a dithiocarbamate fungicide. It is the zinc ion coordination product with manganese ethylene-1,2-bisdithiocarbamate polymer, having the following chemical structure:

Mancozeb has a polymeric structure containing 1.6 percent zinc, in which 6 percent of the units are in the form of a coordination complex. Mancozeb is essentially inert to oxidation by atmospheric oxidation, in contrast with maneb. It is also essentially non-phytotoxic in contrast with maneb, zineb or mixtures of these which are harmful to a number of plants. The standard composition of mancozeb available in the art is an 80 percent wettable powder containing 16% manganese and 2% zinc. However, there are many disadvantages associated with the use of a powder composition. For example, U.S. Pat. No. 5,001,150 discloses removal of disadvantages associated with powder composition and teaches a non-dusty spray dried Mancozeb water dispersible granules (WDG) and the process for their production.
Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) having chemical structure as below is a polychlorinated aromatic mainly used as a broad spectrum, nonsystemic fungicide, with other uses as a wood protectant, pesticide, acaricide, and to control mold, mildew, bacteria, algae. Chlorothalonil-containing products are sold under the names Bravo, Echo, and Daconil. It was first registered for use in the US in 1966. In 1997, the most recent year for which data are available, it was the third most used fungicide in the US, behind only sulfur and copper, with some 12 million lb used in agriculture alone that year. The EPA estimates, on average, almost 15 million lb were used annually from 1990-1996, including the non-agricultural uses.

The article titled “Fungicides to Control Early and Late Blight on Russet Norkotah Potatoes” Steven R. James and Frederick J. Crowe, discloses an experiment to evaluate the efficacy of selected fungicides on early and late blight control on Russet Norkotah potatoes. The article discloses Dithane+Bravo WS at the rate of 3.20 pt/a+1.50 pt/a (Dithane-mancozeb, Bravo-Chlorothalonil) and Dithane/Bravo 3.2 pt/a applied individually. It was observed that there were no significant differences (p<5%) among the fungicide treatments except for the week of August 30 when more early blight infected plants were observed in the Dithane/Bravo (mancozeb/chlorothalonil) when applied individually. Therefore, although the combination of mancozeb with chlorothalonil is known, the precise concentrations at which the combination shows proper synergistic effect in treating fungal infection is not known.
JP 56-046804 discloses antifouling agent composed of an insoluble salt of dithiocarbamic acid and tetrachlorophthalonitrile at 1/1 ratio, thus showing low toxicity and giving no adverse effects on, e.g., the storage stability of antifouling paint preparations, color and coating films. The disclosed antifouling agent is used by mixing or dispersing it in resins for general coating such as natural resin, oil mixture, synthetic resin or synthetic rubber, when necessary, together with pigments and plasticizers. The resulting preparation is applied to the materials contacting with water such as ship bottom, fish net and other underwater constructions to prevent them from fouling by aquatic lives such as sea weeds or barnacle.
The use of fungicide combinations is a widespread and documented practice in the agricultural community. Fungicidal combinations offer significant advantages over individual applications including improved and extended fungal control, reduced fungicide application rates and costs, shorter contact times for improved results, less stringent use restrictions, improved selectivity, improved spectrum of fungi controlled, reduced cost and reduced residue problems. However, identifying appropriate fungicide application rates and ratio of the combinations is essential to achieve efficacious weed control. Hitherto, there have been no studies to determine the most-efficacious and synergistic ratios of mancozeb and chlorothalonil, at which ratio these fungicides synergistically complement each other's fungicidal properties not seen at other ratios.
Even though the combination of Mancozeb and chlorothalonil is known in the art, the same is not known to be synergistically effective in combating the fungal diseases. Thus there exists a need in the art for a composition comprising Mancozeb and chlorothalonil at a ratio which shows superior and effective control on fungal infections.